Sound picture apparatus



l FaizentedJan. 7, 1936` PATENT OFFICE SOUND PICTURE APPARATUS Edwin H. Smythe, Evanston, Ill., assignor to Bell Telephone Laboratories, Incorporated, `New York, N. Y., a corporation of New York Application July 25, 1931, Serial No. 553,144

Renewed May 3, 1934,

is claims. (ci. :r11-2.3)l

This invention relates to sound picture apparatus and more particularly to a driving mecha- Vnism for driving the sound reproducing or record.

iing part of the apparatus.

.I i well known type of apparatus of this sort in 'which sound and scene are'reproduced synchronously involves driving from a common source, 'a motion picture projector and a sound sprocket acting upon the lm after it leaves the rojector head. AThe sound sprocket serves to pr sent an edge of the film in operative relation to an electrical reproducing or recording device for reproducing or recording the sound, the record in this .case being placed on the edge of the nim. In apl5 paratus of this general character, it is important that not only the sound and picture mechanisms be operated in synchronisni but that the sound record be presented to the sound reproducing device at a uniform lspee since variations inspeed will cause variations in he sound from that originally recorded which takes the form of a rapid variation superimposed on the sound and is commonly called a utter. This flutter is generally due to irregularities in the gear teeth which are ordinarily used to vtransmit motion from the main shaft or common v source to the sound y sprocket. It may also be due to variations in load placed on the sound sprocket by inequality in sprocket hole spacing, variations innlm thickness and oil or dirt on the lm.

One method which has been used to minimize this iluttering effect is to place a heavy ilywheel on the shaft with the soundsprocket. Fly- Wheels, in order to be effective for this purpose,

must have considerable mass and consequently are of considerable size'and take up considerable space. In the driving device of the present invention. the flywheel is eliminated as is the gear 40 type drive, the advantages of the gear drive-and flywheel being obtained without the disadvan tages inherent in such mechanisms. q

In accordance with the invention, the sound sprocket is' -mounted on a shaft which is driven from a parallel main shaft by means of a positive belt drive. The main shaft is rigidly connected tothe armature of the driving motor and has imparted to it the inertia vof the. )motor armature. In order that the sound sprocket may have positively imparted to it the effective inertia of the l motor armature, and, thus render unnecessary the use of afflywheel'on the sound sprocket shaft, it

' is preferred to use a belt in the form of a light steel tape of the so-called weldless type,pro j vided with equally spaced perforations which en- ,gage pins or teeth on thedriving pulleys on the two shafts. other snooth running positive ben; drives might be used, providing they have the property of the steel tape or ribbon belt of being substantially inextensible o r unyielding under the load conditions that obtain and actv to establish 5 rotational rigidity between the motor armature and the sound sprocket. In order to -prevent speed uctuations of the sound sprocket such as might result from transverse belt vibrations, a braking or retarding force is applied to the belt.- 10 In the preferred arrangement, the belt is caused to travel through a fluid, such as oil, which, due to its viscosity, has abraking or vibration damping action on the belt moving through it. A xed and unvarying velocity ratiol is thus main- 15 tained between the motor armature and the sound sprocket.

It is common practice to provide each sound and picture reproducing or recording machine with an individual motor, which arrangement 20 has certain advantages in a machine in which the sound sprocket is gear driven. In accordance with a feature of the present invention, a'common drive for a plurality of machines is utilized-and results in' unexpected advantages. Since a posi- 25 tive belt drive is used, any number of machines may be connected to the main shaft and the inertia of the common driving motor and the main shaft utilized as a steadying means for all of the machines. Where individual motors are 30 used, the inertia of the motors is relatively small compared with the sound sprocket iiywheel, but with a common drive the mass of the motor and the drive shaft is increased and hasrasubstantial steadying influence on the sound sprocket 35 drives.

drive which engages perforations in the lm at or near the sound reproducing equipment, it is used herein in a broader sense to dene a lm 45 handling mechanism at or near the sound reproducing or recording point whether inthe form of atoothed sprocket, a smooth drum, an endless 'Y belt or other similar lin feeding device which is constructed to positively engage and prevent slip- 50.

ping of the film during a portion of its movement.

In the drawing, Fig. 1 represents a view in elevation and partly in section of the driving mechanism of the invention; Fig. 2 is a sectional view across the line 2-2 of Fig.`1; Fis. 3l is an ele- 55 vation showing the driving mechanism of the invention applied to a plurality. of sound picture reproducng machines; and Figs. 4 and 5 are views of a preferred form of the driving belt.

Referring particularly to Fig. 3 whereinA two of the sound' picture reproducing machines are shown in front elevation, the usual adjustable bases are indicated at I, the projector head at 2, the upper. lm magazine at 3 and the lower lm magazine at 4. The lm passes from the upper film magazine 3 into the projector head2 and behind the projecting lens 5 and is driven through the projector head with an intermittent move-l ment through the drive shaft 6 which is positively driven by a suitable belt 'I' from the main shaft 8. This mechanism, except that gear. drive is used instead of belt drive, is common to the standard motion picture projector in common use.

'Howeven the belt drive of the projector mechanism is no part of my invention and the ordinary'- gear drive may be substituted if desired. After 'leaving the projecting lens 5, the lm passes through a suitable number of'idlers and guide pulleys to a sprocket known as the'sound sprocket 23 shown in Fig. 1 which is mounted on the shaft 9. After passing this point, the lm is delivered to the lower lm magazine 4. The main shaft 8 is driven from a source of power I0 which may be a motor which is ordinarily provided withV automatic regulating equipment to keep its speed Furthermore, when the rotor of such a constant velocity motor is connected with the sound sprocket shaft by a positive transmission that does not itself introduce velocity variations, the

` effective inertia imparted to the sound sprocket by the mass of the rotor and its shaft is sufdcient to take care of such variations as have their rise in variations in the frictional force exerted onthe lm by the lm gate or similar irregularities. Contributing to the elimination of these irregu- `larities, is shown in Fig. 3 a plurality of reproducing machines which are driven from a common motor and shaft, which means a heavier motor and shaft than if individual drives are used. By

using such common drives, and properly pro- -portioning the speed and power to the load, ad-

vantage is taken of the inherently greater inertia of the motor and drive shaft tosuppress these small variations.

The main drive shaft is rigidly coupled with the reproducing machine when desired by means ofthe clutch 2l the driving member of which is keyed to theshaft 8 and the driven member of 'which is keyed to the sleeve 28 withinwhich the shaft 8 rotates. This sleeve carries the driving sprocket I3 for the soundhead and the driving sprocket 29 for the picture head or projector. 'Ihe driving sprocket I3 is vcoupled with the sound sprocket shaft by means of the positive belt drive of the invention, one embodiment of which'is shown in Fig. 1. It consists of a perforated steel belt` or band II preferably of the weldless type passing over the peripheries of two accurately centered and accurately circular sprockets I2 and4 I3 carrying teeth which enter the spaced perforations in the band. In accordance with the l practice customary in .the movement of perfoin the spacing of the perforations. A high de- .weldless type of belt.

rated film, the sprockets I2and I3 are provided with strippers (not shown) to insure the smooth ldisengagement of the belt from the sprocket teeth. The sprockets I2 and I3 are located,*as

shown. in the opposite ends of the casing I5; one 5 end of which embraces the main shaft 8 and sleeve 28, and the other end of which embraces the shaft 9. The sprockets I2 and I3, it will be understood, will have their diameters so related as to give A`the desired velocity ratios between the driving 10 and driven members. This, in the case of the system described in the paper by Stoller already mentioned, is a speed reduction ratio of 20 to 6 as between the motor armature and the sound sprocket. In its preferred form the belt II is 15 constructed-as illustrated in Fig. 4 and Fig. 5. The longitudinal edges 24 of the perforations 25 are upset from the-plane of the belt and are shaped on the contour. of an involute curve to conform with the contour of the sprocket tooth. 20 The separation between the elastic `upset edges 24 is slightly less than the breadth of the sprocket tooth at the point of engagement so that the teeth and perforations will tend to be smoothly centered ywith respect to eachother during the engaging 25 movement. The perforations in the belt and the teeth in the sprockets are closely spaced to obtain -the advantage of the constant engagement of a large number of perforations and sprocket teeth for insuring a uniform flow vof velocity from the 30 motor armature to the sound sprocket and the elimination of. troublesome low frequency disturbances. Any slight tooth and perforation disturbance which may be produced will have a high frequency characteristic and therefore be readily 36 suppressed by damping and elasticities of a known character which may be introduced in the transmission system.

If desired, the transmission between the driv'- .ing motor armature and the sound sprocket may 4o be through the vmedium of a exible belt of steel or metal provided with simple substantially rectangular perforations such as are well known and commonly usedin motion picture film pro- 'vided the flexible .belt has properties similar to 45 the endless steel belt with respect to longitudinal -rigidity of the belt. The longitudinal rigidity of an endless belt of steel ribbon or the like makes it possible to exercise a high degree of accuracy -tary interlock between the sound sprocket and the motor armature. Thus, there is Aprovided a xed speed reduction means for positively cou.- pling the sound sprocket to the effective inertia of the motor armature.

If desired, a metal belt of the character disclosed may be accurately perforated and formed by joining the two endstogether by means of a dovetailed electric weld ina manner well understood in the electrical welding art. This provides substantially the same longitudinal rigidity and uniform continuity that characterizes the The shaft 9 lies within the pivoting axis of the projector so that the projectormay be adjusted at different angles without disturbing the relation of the main shaft 8 and the shaft 9. A spring A pressed roller`may engage the projector belt I 7s aosmov to take up any slack due to pivoting adjustment of the projector.;

the upper part of the casing from which it returns by way of the clearance space between the cas-v ing walls and the two sides of the belt. Oil in the `upper part of the -casing that may leak through the inner bearing of the sound sprocket shaft 8 flows by gravity to pipe 20 and returns together with any leakage through the inner bearings of drlveshaft 8, to bottom of the casing.

It will also be observed that the pumpkeeps the oil above the level of the upper end of pipe 20 so that the entire casing, including the shafts 4through which the belt moves, will be filled with oil. Thebelt II therefore moves in abath of heavy oil and the high vviscosity of such oil with reference to thebelt serves as a brake or damper to suppress minute variations in the position of the belt..

As .shown more particularly in Figs. l and 2 the casing for the belt of the drive may be conveniently formed of two casings 2l and 22. These two casings when assembled,form4 an upper and `lower chamber and two channels connecting such chambers through which the belt runs with its surfaces close tothe inner walls of the channels.

' vide and maintain the oil fllm between' the belty and its cooperating surfaces. A viscosity or ohmic resistance load may, if desired, be added tothe sound sprocket shaft to further reduce velocity variations by locating a stationary member or surface of the casing in close proximity to a rotating surface of the upper sprocket I2 with an intervening illm of'oil.

A convenient form of sound flmlfeeding'sprocket is indicated at 23 and is known as the sound sprocket because the nlm at or adjacent that point is presented to the sound reproducing mechanism. By virtue of the positive drive of the invention, the sound sprocket moves with the same uniform speed as the main drive shaft and the braking or damping effect of the o il on the moving parts contributes to and aids in the further elimination of any slight variation in speed due to variations of the load caused by the lm.

It is obvious that the constant speed drive disclosed herein as applied to a sound picture reproducing machine is equally applicable to machines for recording sound and scene and to machines for separately recording or reproducing sound independently of scene. y

' What is claimed is:

1. A constant speed film driving mechanism for sound picture apparatus comprising a flmdriving sprocket having a pulley rigidly connected thereto, a main drive shaft having a pulley rigidly connected thereto, a belt arranged to positively engage said pulleys, a resistance fllterarranged to resist forward or backward velocity the well 28 in the for sound picture apparatus comprising a filmy drivingsprocket having a pulley rigidly connected thereto, a main drive shaft having a pulley rigidly connected thereto, a belt arranged to positively engage said pulleys, a fluid resistance lter 5 arranged to resist forwarder backward velocity variations comprising a casing enclosing said pulleys and belt supplied with a viscous fluid 4whereby said belt and pulley may be directly sub- `jected -to the filtering action of said resistance.

3. A constant speed driving mechanism for for feeding a record strip to a recording or reproducing instrumentality, comprising a feed sprocketr to engage perforations in the 'record 15 strip, a shaft for said sprocket, a drive shaft, a belt forv positively driving the sprocket shaft from the drive shaft, anda resistance applied to the surfaces of said belt for imposing on said record feeding means a braking force which is large compared to the load variations imposed on said feed sprocket by said `record strip said resistance being arranged to oppose forces influencing forward or backward velocity variations. I

4. A constant speed driving mechanism for sound recording or reproducing apparatus including means for feeding a record surface to recording' or reproducingv instrumentalities, means for driving said record feeding means comprising a drive shaft, a driven shaft and a belt positively connecting said shafts; and a resist- `ance applied to the surfaces of said belt for im- -posing on said driving means a braking or retarding force'which is large in comparison to the load variations imposed on said drive by irregularities in the record feeding operation said resistance being arranged to oppose forces influencing forward or backward velocity variations. `5. A constant speed film driving mechanism for sound picturey apparatus comprising a film d nv- 40 ing sprocket having a pulley rigidly connected thereto, a main drive shaft having a pulley rigidly connected thereto, a beltarranged to positively engage said pulleys, a uid resistance filter arranged to resist forward or backward velocity variations comprising a casing enclosing said pnl leys and belt supplied with a viscous uid with such positional relation between the belt and walls of said casing as to establish a large resistance to the forces influencing velocity variations.

6. A constant speed lm driving mechanism for sound picture apparatus comprising a. lm driving sprocket having a second sprocket rigidly connected thereto, a main drive shaft having a sprocket rigidly :connected thereto, an endless belt having -perforations therein connected be-` tween said second sprocket and said drive shaft sprocket, a resistance lter arranged to resist forward or backward velocity variations and means whereby said belt may be directly subjected to the lterlng action of said resistance.

7. A constant speed fllm driving mechanism for sound picture apparatus comprising a film driving sprocket having `a second sprocket rigidly connected thereto, a main drive shaft having .a sprocket rigidly connected thereto, an endless belt having perforations therein connected between said second sprocket and said drive shaft sprocket, a fluid resistance filter arranged to resist forward or backward velocity variations and 7o means whereby said belt may bev directly subjected to the filtering action of said uid resistance.

I 8. A constant speed nlm driving mechanism for sound 4picture apparatus comprising a nlm 75 ,driving sprocket having a second 'sprocket rigidly connected thereto, a main drive shaft having a sprocket rigidly connected thereto, an endless belt having periorations therein connected between said second sprocket and said drive shaft sprock' et, a resistance lter arranged to resist forward or backward velocity variationscomprising a casing enclosing said' belt supplied with a viscous uid whereby said belt may be directly subjected to the filtering action of said resistance.

. 9. `A constant speed lm driving mechanism li'or sound picture apparatus comprising a. nlm driving sprocket having a second sprocket rigidly 'connected thereto, a main drive shaft having a sprocket rigidly connected thereto, an endless metal belt having perforations therein connected between said second sprocket and said drive shaft sprocket, the edges of said perforations being shaped on the contour of an involute curve to .10 conform with the contour of the sprocket teeth..

a resistance tllter arranged to resist forward or backward velocity variations comprising a casing enclosing said belt supplied with a viscous iluid 'with such positional relation between the belt and 25 walls of said 4casing as to establish a large re- .sistance to the forces influencing' velocity variations. I

10. In sound picture apparatus having'a constant speed driving motor and a. sound sprocket 30 for moving the sound lm, means i'or establishing rotational rigidity between the sound sprocket and the inertia ofthe motor including a toothed driving sprocket on the motor amature shaft,

. a toothed driven sprocket on the sound sprocket I 3-5 shaft, and a longitudinally -unyielding metal belt with perforations in said' metal shaped to con- .form accurately with the contour of the sprocket n teeth.

11. In sound picture apparatus having a constantspeed driving motor and a sound sprocket for moving the sound iilm, means for establishing rotational rigidity between the sound sprocket and the inertia of the motor including a, toothed 5 ,driving sprocket on the motor armature shaft, a

toothed driven sprocket on the sound sprocket shaft, and a longitudinally unyielding metal belt with perforations in said metal with sides protruding beyond one surface of the metal of the beit 1o shaped on an involute curve to conform accurately with the contour of the sprocket teeth.

12. In sound picture apparatus having a constant speed driving motor and a sound sprocket for moving Athe sound nlm', means for establishing l5 rotational rigidity between the sound sprocket and the inertia of the motor including a toothed l driving sprocket on the motor armature shaft, a toothed driven sprocket on the sound sprocket shaft, a. longitudinally unyielding metal belt with periorations in saidnetal shaped to conform ac' curately with the contour of the sprocket teeth, andV means to apply resistance to said belt for damping load variations.,

13. In a sound picture appmatus having a' constant speed driving motor and a sound sprocket for moving the sound nlm, a non-slipping belt transmission' between the driving motor and the sound sprocket including a driving and a driven sprocket1with teeth spaced as-closely as practical, $0

n and a'perforated metal ribbon belt between said driving and driven sprockets with perforations spaced and shaped to accurately match the spacing and contour of the, sprocket teeth to provide a rotational rigid coupling between the driving 3lmotor and the sound sprocket.

EDWIN H. SMYTHE. 

